VCO3_NAJKA
Function
Complement-activating protein in cobra venom. It is a structural and functional analog of complement component C3b, the activated form of C3. It binds factor B (CFB), which is subsequently cleaved by factor D (CFD) to form the bimolecular complex CVF/Bb. CVF/Bb is a C3/C5 convertase that cleaves both complement components C3 and C5. Structurally, it resembles the C3b degradation product C3c, which is not able to form a C3/C5 convertase. Unlike C3b/Bb, CVF/Bb is a stable complex and completely resistant to the actions of complement regulatory factors H (CFH) and I (CFI). Therefore, CVF continuously activates complement resulting in the depletion of complement activity.
Post-translational modifications
First processed by the removal of 4 Arg residues by furin-type protease, forming two chains, alpha and gamma/beta precursor, linked by a disulfide bond. Probably, the cobrin cleaves the C3a-like domain and then the C3d-like domain, generating the mature cobra venom factor (CVF). This mature CVF is composed of three chains: alpha, gamma and beta.
Contains 3 N-linked oligosaccharide chains, two in the alpha-chain and one in the beta-chain. Glycosylation is not required for the biological activity. However, it contributes to the immunogenicity of CVF. The carbohydrate content is 7.4. The major oligosaccharide is a symmetric fucosylated biantennary complex-type chain with an unusual alpha-galactosylated Le(x) structure at its non-reducing end.
Sequence Similarities
Belongs to the venom complement C3 homolog family.
Tissue Specificity
Expressed by the venom gland.
Cellular localization
- Secreted
Alternative names
Cobra venom factor, CVF, CVFk, Complement C3 homolog